The invention relates to an optical image-magnifying element having a Fresnel lens, and a plurality of such elements, arranged in rows and columns. The assembly produces a plurality of separate mutually spaced pictures, reproduced by separate picture tubes, to form one unitary picture without discontinuities. The invention also relates to an information-display unit provided with such an image-magnifying element and to an information-display panel comprising a plurality of such units.
The information-display panel, which is also referred to as "video wall" or "super large-screen television", is currently used for displaying information, such as entertainment programs, instructional programs, commercials, still pictures containing messages of miscellaneous kinds, in large species, for example those where exhibitions are held, to a large public. The display panel may have a surface area varying between, for example 2 m.sup.2 and 200 m.sup.2 and a depth of the order of 0.5-1 m. Such a panel comprises a plurality of conventional picture tubes arranged in rows and columns, the number of picture tubes being dependent on the desired size of the panel picture.
Such a panel may be employed for simultaneously reproducing a plurality of different pictures of equal or different size, which are each reproduced by an equal or a different number of picture tubes, but also for the reproduction of one large picture, in which case each of the picture tubes displays a separate part of the total picture. In such a case, unless further steps are taken, the desired visual impression of a single picture is disturbed by discontinuities because the viewing screens or effective screen surfaces of the picture tubes are spaced from each other. This is because the picture tubes are acommodated in housings having walls of a specific thickness and because the viewing screens cover only part of the face plates of these picture tubes, since the viewing screens have borders.
Another problem associated with the display panel is that the screens of the picture tubes are curved, whereas until now the panel surface which faces the spectators should preferably be flat.
European Patent Application No. 0,074,696 describes several possibilities of reducing the discontinuities in the panel picture and of compensating for the face plate curvature. For example, a multitude of light-conducting fibres may be arranged on the face plate of a picture tube, which fibres fan out towards the audience and thus provide an image-magnifying effect. As a result of this magnification the constituent pictures forming the panel picture adjoin each other without any discontinuities. This solution is particularly suitable for a panel to be viewed from a large distance; in the case of smaller viewing distances the picture elements formed by the individual light-conducting fibres will be visible on the panel. On account of the desired magnification the fibres should have a specific length, so that the fibre array has a considerable thickness and consequently a comparatively large weight. The manufacture of fibre arrays, in particular if the fibres are required to have conical shapes, is rather difficult and therefore expensive when current technologies are used.
As is also stated in European Patent Application No. 0,074,696, the desired magnification of the individual pictures on the picture tubes can also be achieved by means of plane Fresnel lenses, one such lens being arranged in front of every picture tube. However, when a plane Fresnel lens is employed for imaging the picture displayed on a curved screen the picture will become distorted. Moreover, the problem of accurately positioning the Fresnel lens relative to the associated picture tube still has to be solved. In addition, the transitions between the individual Fresnel lenses are still visible in the panel picture.